The addition of polymers to powder-form detergents often leads to a deterioration in storage stability, the detergents agglomerate and lose their flowability. Because of this, the polymers are preferably used in the form of granules. Accordingly, the production and use of polymer-containing granules is the subject of numerous literature references.
European patent application EP-A0 759 463 describes detergent compositions consisting of a basic powder to which commercially available granules of a polycarboxylate copolymer (for example Sokalan CP5®) are subsequently added. The subsequent addition of the polymer in granular form stabilizes the bleaching system by comparison with compositions where the polymer is present in the basic powder.
An additive for detergents containing 20 to 80% by weight polymeric polycarboxylate besides 20 to 80% by weight nitrilotriacetate is described in U.S. Pat. No. 4,698,174. The function of the nitrilotriacetate is to reduce the hygroscopicity of the polycarboxylate.
EP-A0 368 137 and DE-A-33 16 513 are concerned with zeolite granules which also contain polycarboxylate polymer. The granules according to DE-A-33 16 513 are produced by spray drying and contain polymeric polycarboxylates in quantities of at least 5% by weight to reduce the abrasion of the zeolite granules. EP-A0 368 137 describes a process for the production of granules containing 2 to 15% by weight polycarboxylate. A homogeneous powder-form mixture is first prepared from the zeolite and the polycarboxylate and then agglomerated and the agglomerate obtained is dried.
WO 94/13775 relates to a process for the production of powder-form detergents containing polyvinyl pyrrolidone (PVP). In order to maintain the flowability of the detergent, the PVP is added to the powder-form detergent containing the other detergent ingredients completely or partly in the form of a separate mixture (PVP concentrate) with other powder-form detergent ingredients. The PVP concentrate may contain 10 to 50% by weight PVP and preferably 40 to 80% by weight inorganic carrier salts besides small quantities of water. These concentrates are preferably produced by spray drying.
A detergent additive containing 15 to 60% by weight PVP, 5 to 90% by weight carrier material, 5 to 60% by weight salt and 0.5 to 30% by weight binder is described in EP-B0 652 937. The additive is produced by mixing PVP, carrier and salt and then spraying on the binder. The advantage of this additive is that detergents which contain it do not agglomerate as quickly as comparable compositions to which PVP is directly added because the carrier material first binds with the moist PVP.
A discoloration-inhibiting detergent additive which contains at least partly water-soluble polymer constituents based on N-vinyl pyrrolidone or N-vinyl imidazole or N-vinyl oxazoline in combination with a cationic compound and which is odorless, even in combination with alkaline detergent ingredients, is described in EP-A0 327 927. This additive is obtained by mixing the starting materials together and drying the resulting mixture with heated air.
European patent application EP-A0 421 664 is also concerned with granules that can be used in detergents. The granules contain at least 10% by weight of polymer and at least 20% by weight of a water-soluble inorganic component or at least 20% by weight of polymer in addition to at least 20% by weight of a water-insoluble inorganic component and have a bulk density of at least 700 g/l. Preferred granules contain 20 to 40% by weight of polymer. The granules are produced by mixing a solution or a slurry of the polymer with the inorganic component and granulating the resulting mixture in the presence of heat.
European patent EP-B0 658 189 describes detergents which contain at least two granular components, one component being a granular admixing component of polymeric polycarboxylates. The polymer granules have a bulk density of 350 to 850 g/l and are conventionally produced, for example by drying of polymer solutions, subsequent granulation and optionally sizing/grading. The polymer solution is preferably dried in a spray drying tower or in a fluidized bed. Unfortunately, the patent specification in question does not provide exact details of the production process or the composition of the polymer granules.
The granules known from the prior art generally have low polymer contents or contain additives which are intended to limit the hygroscopicity of the compounds and hence their water content. None of the processes described hitherto is generally suitable for the production of granules of polymeric detergent ingredients which have a high polymer content, are readily soluble, stable in storage and free-flowing and—carriers apart—contain no other additives.
Accordingly, the problem addressed by the present invention was to provide a process which would be suitable for the production of readily soluble, flowable and carrier-containing granules with high polymer contents.